1. Field of the Invention
The present invention generally relates to an amplifying system for a solenoid controlled proportion valve used in a hydraulic system, and more particularly to an intelligent amplifying system having a fault diagnosis function and a protective function in the hydraulic system.
2. Description of Prior Art
FIG. 1 shows a schematic view of a mechanism for controlling a conventional solenoid controlled proportion valve, in which an amplifying circuit 1 for the solenoid controlled proportion valve (hereinafter, referred to as "proportion valve") controls an operation of the proportion valve in response to operating signals provided from operating members such as an electric joystick 2, an electric pedal 3, and an external controller 4 having a function similar to those of the members 2 and 3.
When an electric current is transmitted from the amplifying circuit 1, to the proportion valve 5, a spool (not shown) in the proportion valve 5 moves in response to the transmitted amount of an electric current. Accordingly, an oil pressure (or a flow amount) can be controlled by a displacement of the spool.
FIG. 2 illustrates a conventional analog amplifying circuit.
Referring to FIG. 2, the operating signal provided from operating members (see reference numerals 2, 3 and 4 shown in FIG. 1) is transmitted to the amplifying circuit 1 through an input terminal 31. The input signal is then transmitted to four limiters 36, 36a, 36b and 36c composed of Schmidt trigger circuit, respectively.
The first trip point setting unit 32 determines the lower trip point which corresponds to 10% of the input signal amplitude. The limiters 36 and 36b operated by the first trip point setting unit 32 and inverters 35a, 35b, 35c put the first proportion valve 1 into an enable state and the second proportion valve 5a into a disable state when the input signal is above the first lower trip point.
The function of limiters 36 and 36b, for example in hydraulic equipments, is accomplished in such a way that in its forward move the first proportion valve is put to enable state with the second proportion valve put to disable state, and in its backward move each valve is put to the opposite state, respectively.
The upper trip point corresponding to 90% of the input signal is determined by the second trip point setting unit 32a. When the input signal is higher than the first upper trip point (90%) or lower than the second upper trip point (-90%), the range limiters 36a and 36c allow a maximum amount of current (I limit) to be transmitted to the proportion valves 5 and 5a as shown in FIG. 3 which represents input/output characteristic graph of amplifying circuit 1.
An offset current (I offset) shown in FIG. 3 is set by an offset setting unit 33, and an amplitude of the offset current (I offset) can be controlled by a variable resistor (not shown). The input signal provided from the operating means through the input terminal 31 to the amplifying circuit 1 is transmitted to two adders 38 and 38a after the input signal has been controlled to take a predetermined gain determined by a gain adjusting member 34.
A dither generator 37 is employed to make use of the principle that it is easier to move the moving body than to move the fixed body. The dither generator 37 generates a dither signal for enhancement of mechanical response characteristics by trembling each spool of the proportion valves 5 and 5a with a very small displacement. The dither signal is a voltage signal of a triangular wave having a predetermined frequency and amplitude.
The adders 38 and 38a add the offset signal to the output and dither signals of the gain adjusting member 34 while the adder 38a receives an inversion output of the gain adjusting members 34 through an inverter 35, 35a, 35b and 35c.
An output signal controllers 39 and 39a are operated in such a manner that the ratio of output signal to input signal in the amplifying circuit 1 is kept constant based on a signal provided from a current sensor 40 which detects a current amount supplied to the proportion valves 5 and 5a.
Pulse width modulators 42 and 42a compare the output signals of controllers 39 and 39a with those of current limiters 41 and 41a which prevent an overcurrent from flowing and that of a carrier generator 43 generating a triangular wave, and then, from the above comparison, generate a pulse width modulation wave of a variable duty.
Current supplying units 44 and 44a can be subject to ON state or OFF state depending on the output of the pulse width modulators 42 and 42a, so that the current amount supplied from a power supply (not shown) to the proportion valves 5 and 5a can be controlled.
Accordingly, the operation of the proportion valves 5 and 5a are controlled by the current amount supplied by way of the current supplying units 44 and 44a.
In the conventional analog amplifying system mentioned in the above, in order to perform a gain adjusting, an amplitude setting of the offset signal, a frequency and amplitude adjusting of dither signal, etc., the values of variable resistors included in the offset setting portion 33, the gain controller 34 and the dither generator 37 respectively should be adjusted one by one by a trial and error method.
However, such a conventional parameter control method has drawbacks that it causes the reduction of the yield of products and lowers the reliability of products. In addition, since the conventional system is comprised of only analog elements in a whole system, it has a complicated structure.
In particular, if the proportion valve is replaced with that of another model, it is impossible for the ordinary experts to reset parameters working with the replaced valve.
Also, in the conventional system, there is not provided a safety mechanism for preventing an accident if, for example, the equipment is erroneously operated due to an undesirable contact with input operating elements when an operator gets in and out of the operation seat.
Thus it would be desirable to provide a safety device for preventing the accidents in driving the system.
In addition, the conventional system is not provided with a failure diagnosis function which is capable of managing effectively the accidents when the system errors occur.